164 ANNUAL OF SCIENTIFIC DISCOVERY. 



land and Basilisk, which were both constructed on the same principle, 

 with oscillating cylinders, and were both used to drive paddle-wheels. 

 This comparison was made under three distinct heads ; the mean 

 effective pressure, the number of revolutions per minute, and the size 

 of the cylinders. It was urged that Watt's constant of seven pounds 

 per square inch, for the mean effective pressure, was not only in itself 

 inapplicable, but that no constant quantity could be universally appli- 

 cable. Also, that the method of* determining the number of revolutions 

 per minute from a conventional speed, founded on the length of the 

 stroke of the piston, was equally fallacious. It was, therefore, proposed 

 that the term, "nominal horse-power," should be abolished; that 

 engines should in future be designated by the cubic contents of their 

 steam-cylinders, jointly with their nominal consumption of a standard 

 description of fuel, during a given period of one hour. The system, it 

 was contended, would be more in accordance with the present practice 

 of construction, and would enable the relative size and power of engines 

 to be more accurately estimated than by the present method. In the 

 ensuing discussion, it was admitted that it would be very desirable to 

 fix the nomenclature of the power of engines ; for, though it was well 

 known that James Watt did really take as his standard what he found 

 to be actually performed by a powerful horse, drawing a weight over a 

 pulley, viz., the equivalent of 33,000 pounds raised one foot high in a 

 minute, yet, commercially, it had gradually become a custom among 

 manufacturers to give a surplus of power, ostensibly as an allowance for 

 friction and deficiencies of the machine, so that now the mere statement 

 of the nominal horse-power had no definite meaning. It was, however, 

 contended that the standard of 33,000 pounds should be retained ; and 

 that, supposing the workmanship to be equally good in two engines, it 

 was only necessary to compare the areas of the cylinder, the effective 

 pressure of steam on the piston, and the speed of the piston, to deter- 

 mine their relative power. This was, in fact, shown by the indicator, 

 an instrument, the value of which was now universally admitted, and 

 which, when skilfully used, did really give a true representation of the 

 power of the engine. It Avas the universal custom of Boulton and 

 Watt to calculate the power exerted by an engine by the speed of the 

 piston, together with the average pressure of the steam, as shown by 

 the indicator ; and, although much vagueness and uncertainty had lat- 

 terly been introduced into the subject, this was rather to be attributed 

 to the assumption of arbitrary quantities to represent these results, 

 than to any defect in Watt's standard horse-power, which definitely 

 expressed both the measure of power and the space through which it 

 acted. The proposed standard of comparison of the quantity of water 

 evaporated in a given time, by a given amount of fuel, or the combus- 

 tion of a given quantity of fuel in a given time, were shown to be of 

 no value, as then, not only the generation of the steam, but the admin- 

 istration of it, must be considered, and these points merely tend to 

 complicate the question. For pumping-engines in Cornwall, the term 

 horse-power was almost unknown ; engines being sold to raise a given 

 quantity of water, which was a standard easily reducible to that of 

 other districts, where 33,000 pounds was assumed to be the actual 



